1. Field of the Invention
The present invention is directed to a process for cleaning, disinfecting, and sterilizing materials, and, more particularly, to a process for employing the combination of dense phase gas, ultraviolet radiation, and sterilants such as H.sub.2 O.sub.2 to clean, disinfect, and sterilize materials such as fabrics and medical implements.
2. Description of Related Art
(A) Medical and Dental Instruments
In the health field, medical and dental instruments that enter the blood stream or sterile tissue should be sterilized before each use. Sterilization means the use of a physical or chemical procedure to destroy all microbial life and endospores. Today, main hospital sterilizing means are (a) moist heat by steam autoclaving, (b) dry heat, and (c) ethylene oxide gas. However, many medical devices and implements cannot be subjected to heat, as it leads to degradation of the device or implement.
A variety of chemical germicides (sterilants) have been used to process reusable heat-sensitive medical devices, as they promote a high level of disinfection (virtual elimination of pathogenic microorganisms, but not all microbial forms, such as bacterial endospores). There are three levels of disinfection: (1) high (kills all organisms except high levels of bacterial spores with chemical germicides registered as sterilants by the EPA), (2) intermediate (kills mycobacteria, bacteria, and most viruses, with a chemical germicide registered as a "tuberculoside" by the EPA, and (3) low (kills some viruses and bacteria with a chemical germicide registered as a hospital disinfectant by the EPA).
In general, items that only intact skin, such as garments, headboards, blood pressure cuffs, and other medical accessories, can usually be processed by washing with a detergent or using a low level disinfectant.
In all cases, the main chemical sterilization or disinfecting technology involves the use of 12/88% ethylene oxide (ETO)/hydrochlorofluorocarbon (HCFC) mixture, hydrogen peroxide (H.sub.2 O.sub.2) plasma, peracetic acid (C.sub.2 H.sub.2 O.sub.3)/H.sub.2 O.sub.2 plasma, and vapor phase H.sub.2 O.sub.2. More recently, a 10/90% ETO/CO.sub.2 gas mixture has been used, where the CO.sub.2 is a more environmentally "friendly" diluant for the active sterilizing species than the HCFC in the 12/88% ETO/HCFC mixture.
The most efficient of the sterilizing technologies cited are the 12/88% ETO/HCFC and 10/90% ETO/CO.sub.2, as they are conducted at positive operating pressures (10 to 12 psig and 50 to 80 psig, respectively). The other known processes are conducted at sub-atmospheric pressures. The sterilization efficacy of positive pressures against challenge barriers is quoted at 97% on surfaces, but only 44% in the lumen for the 12/88% ETO/HFCF. The other sub-atmospheric technologies cited range lower still, between 32 to 78% on surfaces and 6 to 35% in the lumen. See, MacNeal et al., "Comparison of Health Care-Based Sterilization Technologies: Safety, Efficacy, and Economics", Journal of Healthcare Safety, Compliance & Infection Control, vol. 1, No. 2 (December 1997). Across the board, the substantially lower sterilization efficacy cited for hard to access surfaces such as that of a lumen, is due to the difficulty in cleaning biological debris from cavities prior to sterilization or to the presence of inherently higher levels of bioburden in these cavities. Though the positive pressure in the current systems does not ensure a high level of "kill" in cavities, it is better in overcoming the penetration obstacles to the sterilants in cavities, or in the face of heavy bioburden or biomass.
In addition to the above, the chemical sterilants are highly toxic, and even minor residual levels in the sterilizer, or on sterilized surfaces, can act as irritants to operators or patients.
In summary, the current challenges of chemical sterilization for medical and dental devices is related mostly to difficult to access surfaces such as that of a lumen for the rigorous pre-cleaning required for bioburden reduction, delivery of adequate levels of active sterilant for these "challenged" surfaces throughout the sterilization cycle, ability of rapidly delivering sterilants to these surfaces in order to reduce cycle time, and ability to then deactivate or efficiently separate out the residual sterilizing species to minimize the risk to the operator or patient.
(B) Garments
In the field of commercial garment cleaning/dry-cleaning, typically, garments from multiple customers are co-processed in the same machine-cleaning cycle, posing the risk of some forms of pathogen transmission through garment cross-contamination. Fluids used in conventional garment dry-cleaning do not have disinfecting properties, and disinfection in commercial dry-cleaning is not addressed.
The challenge to the commercial garment cleaning/dry-cleaning is to effect the pathogen destruction within the short agitation steps within the cleaning cycle (typically less than 10 minutes) without leading to the degradation of the fabrics themselves and without producing toxic waste.
(C) Dense Phase Carbon Dioxide; UV Radiation
Dense phase carbon dioxide is an inexpensive and virtually unlimited natural resource that is non-toxic, non-flammable, and non-smog producing. Dense phase carbon dioxide is compressed to either supercritical or subcritical conditions to achieve liquid-like densities, and is often simply termed "liquid carbon dioxide". Liquid carbon dioxide exhibits solvating properties typical of hydrocarbon solvents. Its properties make it a good organic solvent-like cleaning medium in general, and specifically, a good dry-cleaning medium for fabrics and garments.
U.S. Pat. No. 5,316,591, issued to Chao et al. and assigned to Hughes Aircraft Company, addresses part cleaning by cavitation in liquified gases. U.S. Pat. No. 5,370,740, issued to Chao et al. and assigned to Hughes Aircraft Company, addresses chemical decomposition of organic materials by sonication in liquid carbon dioxide. U.S. Pat. No. 5,013,366, issued to Jackson et al. and assigned to Hughes Aircraft Company, addresses a part cleaning process using phase shifting of dense phase carbon dioxide with or without the aid of UV, sonication, and chemical oxidants. U.S. Pat. No. 5,236,602, issued to Jackson and assigned to Hughes Aircraft Company, addresses a dense phase fluid photochemical process for liquid substrate treatment using UV, with or without chemical oxidants to chemically alter toxic materials into non-toxic species. U.S. Pat. Nos. 5,068,040 and 5,215,592, both issued to Jackson and assigned to Hughes Aircraft Company, address a dense fluid photochemical process for solid substrate treatment using UV, with or without chemical oxidants. U.S. Pat. No. 5,213,619, issued to Jackson et al., addresses a process for cleaning, sterilizing, and implanting materials using high energy (acoustic radiation or non-uniform electrostatic field) dense fluids.
Although each of the foregoing patents addresses cleaning in dense phase carbon dioxide in general, and specifically, organic chemical destruction with the aid of UV, with or without chemical oxidants, the disinfection or sterilization in dense phase carbon dioxide by UV radiation with or without chemical oxidants is not addressed. Furthermore, although U.S. Pat. No. 5,213,619 addresses a process for cleaning, sterilizing, and implanting materials using dense fluids that are energized by a non-uniform electrostatic field and high powered acoustic radiation, costly sterilizing equipment is needed, and more importantly, removal of soil from substrates is not effective.
The initial patent referencing dens phase carbon dioxide as a suitable solvent for garment dry-cleaning applications is that of Maffei, U.S. Pat. No. 4,012,194. Other patents, such as U.S. Pat. No. 5,267,455, issued to Dewees and assigned on its face to The Clorox Company and U.S. Pat. No. 5,467,492, issued to Chao et al. and assigned to Hughes Aircraft Company, also reference liquid carbon dioxide as a suitable garment dry-cleaning medium. Again, these patents fail to address garment disinfection in dense phase carbon dioxide.
UV light has proven benefits in a broad range of applications, including the disinfection of solid surfaces, liquids, air, and photochemical processes. The advantage of using UV light for disinfection lies in the fact that it controls pathogens without the use of harmful chemicals. For example, UV germicidal energy has been used to purify water. UV energy between 180 and 300 nm disrupts the DNA strands of micro-organisms and prevents cell replication. A microbe that cannot replicate dies. Microbes are particularly vulnerable to the effects of light at a wavelength at or near 253 to 254 nm, due to the resonance of this wavelength with molecular structures. This resonance breaks organic molecular bonds which in turn translate to cellular or genetic damage for microorganisms.
A major disadvantage of this photochemical destruction is that the targeted area must be in the line of sight of the radiation, in order for sterilization to occur and is thus by itself ineffective for all but relatively clean and directly irradiated targets. Addition of oxidizing species that can be readily photo-dissociated upon exposure to the UV radiation into more active species increases the efficacy of the UV sterilization, but it does not resolve the challenge of cleaning hard to access cavities and holes, such as that of a lumen, or the challenge of efficiently delivering the sterilants into these holes.
It is desirable to provide a single-step dense gas cleaning process that, in addition to cleaning a substrate, also achieves the disinfection and sterilization of substrates using simple, faster, economical, and less toxic techniques. The present invention fulfills these needs.